The present invention is directed to a tool for insertion into a tool bit chuck of a manually operated tool used for cutting and/or percussion drilling and includes an axially extending chucking shank with a free end and at least one locking groove closed at its end spaced apart in the axial direction, at least one axially extending groove open at the free end of the chucking shank and located substantially diametrically opposite the locking groove. In addition the clamping shank has two rotary entrainment grooves open at the free end of the chucking shank and positioned substantially diametrically opposite one another and each has a transverse cross-sectional area and an opening extending circumferentially in the outside surface of the shank of a different size with respect to the other.
At the present time, tool bits as disclosed in DE-PS 25 51 125 are in widespread use worldwide and include chucking shanks having two locking grooves closed at their ends spaced apart in the axial direction and located diametrically opposite one another along with two rotary entrainment grooves open at the free end of the chucking shank and also located diametrically opposite one another. The locking grooves have the same cross-sectional dimensions as do the rotary entrainment grooves.
The above-mentioned tool bits are used in manually operated tools with tool bit chucks containing two axially extending entrainment strips as well as two radially displaceable locking elements. The entrainment strips are intended to seat within the rotary entrainment grooves for transmitting torque. The radially displaceable locking elements, in the form of balls or rollers, cooperate with the closed-ended locking grooves and serve for securing the tool bit in the axial direction within the tool bit chuck.
Since particularly high strength requirements are not needed for the axial retention of the tool bits in the tool bit chucks, the use of a single locking element has come into increased use instead of two locking elements. In such axial securement it is attempted to ensure that the tool bit does not become disengaged accidentally from the tool bit chuck, so that in particular on building sites there is no danger of the tool bit dropping out of the tool bit chuck. In addition, the axial securement serves to retain the tool bit within the chuck of the manually operated tool when the tool bit is removed from a structural part after its working operation is complete.
Considerably higher strength requirements are needed for transmitting torque. Particularly, due to the larger working diameter of the tool bit coming into increased use along with the increase in output of the manually operated tool, increasingly higher torques must be transmitted. Such characteristics result in premature wear occurring in the chucking shank of the tool bit, especially in the region of the rotary entrainment grooves and such wear takes place considerably in advance of the normal wear of the remaining parts of the tool bit.
To eliminate these problems, especially regarding higher torques to be transmitted, it has been proposed in DE-A-39 41 646 to provide one of the rotary entrainment grooves with a larger cross-sectional area. This feature enables the enlargement of the cooperating entrainment groove in the tool bit chuck so that a reserve is afforded for higher wear.
In addition to the increased cross-sectional area, it has been. proposed in DE-A-39 41 646 to provide an axially extending groove open at the free end of the chucking shank. The axially extending groove permits the use of a corresponding axially extending strip in the tool bit chuck cooperating with the axially extending groove, so that an additional flank is available for transmitting torque.
All of the above-mentioned features have their justification and advantages if tool bits are used in matching or corresponding tool bit chucks. As indicated above it must be taken into consideration, because of the tool bits previously in use, that manually operated tools have been in general use worldwide in which the chucks have two entrainment strips of the same cross-section and one or two radially displaceable locking elements. Accordingly, it is important to design tool bits formed for transmitting higher torques so that they are compatible with the tool bit chucks in manually operated tools commercially available at the present time, even while neglecting the advantages achieved with the new tool bits.
A serious disadvantage of the previously mentioned tool bit with only one axially extending groove in the chucking shank is that it cannot be used in manually operated tools in which the tool bit chuck has two locking elements, since the second locking element cannot enter into the axially extending groove. If the tool bit is used in a tool bit chuck with only one locking element there is the possibility with entrainment strips of the same cross-section of introducing the tool bit turned through 180.degree.. Because of the existing clearances for the flexural support of the locking element it is possible that radial displacements can be effected, so that the locking element enters into a partially quite strong frictional lock with the chucking shank. An operator cannot readily recognize such faulty locking, since the frictional lock resists the routine checking operation used for determining the proper axial securement. The accidental disconnection of the axial securement of the tool bit in the tool bit chuck takes place unexpectedly and in an undesired manner in use, so that the possibility of accidents cannot be excluded.